Crocodile shark description

A particularly small, slender and distinctive shark (2)(4), the crocodile shark is named for its prominent, spike-like teeth, and its habit of snapping vigorously when removed from the water (3). The spindle-shaped body is grey-brown above, sometimes with white or black blotches, and lighter on the underside, with white margins on the fins (3)(4). The head is relatively short, with a pointed snout, protrusable jaws, long gill slits, and huge eyes, which lack nictitating membranes(2)(3)(4)(5). The dorsal fin and pectoral fins are small and spineless, and the tail fin is asymmetrical, with a long upper lobe (2)(3)(4).

Related species

Crocodile shark biology

The body shape, large teeth and large eyes of the crocodile shark suggest that it is a relatively active predator that hunts by night or in deep water (2)(3)(4). The diet is thought to include relatively large and active oceanic prey such as fish, squid and shrimp, and there is some evidence that this shark undertakes a daily vertical migration, following prey towards the water surface at night and away from it during the day. Although not regarded as dangerous to humans, the crocodile shark is reported to have a strong bite (2)(3).

Like other Lamniformes, the crocodile shark has an unusual method of reproduction, known as uterine oophagy, in which the embryonic young eat the other eggs and young within the female’s uterus (2)(3)(4)(6). The result of this cannibalism is the production of a small number of large, well-developed young (6), typically four per litter in this species (two surviving per uterus). The young are born live, and measure around 40 centimetres at birth (2)(3)(4)(6). Male crocodile sharks may reach sexual maturity at a minimum body length of 74 centimetres, and females at 89 centimetres (3)(6).

Crocodile shark status

Crocodile shark threats

Unlike many other shark species, the crocodile shark is not valued commercially for its large, squalene-rich liver (5), is considered too small to be of much value for its fins, and is little utilised for its flesh (2)(6). However, it may be vulnerable to bycatch in long-line fisheries (1)(2)(3). The population trends of the crocodile shark are currently unknown, but the species is predicted to undergo a decline as long-line fisheries increasingly expand into the open ocean. The small litter size and low reproductive rate of this and other Lamniformes makes them particularly vulnerable to any threats (1)(6), and, because the crocodile shark is generally discarded and unrecorded when accidentally caught (6), it remains difficult to monitor its conservation status.

Crocodile shark conservation

There are no known conservation measures in place for the crocodile shark (6). The biology of this species is poorly known, and it has been recommended that catches be reported and preserved in order to learn more about it (3). As assessments of the populations of this species are lacking, some advise that a cautionary approach be taken by international fisheries to ensure that vulnerable species such as the crocodile shark are not unnecessarily threatened (7).

Authentication

Glossary

In the fishing industry, the part of the catch made up of non-target species.

Dorsal fin

The unpaired fin found on the back of the body of fish, or the raised structure on the back of most cetaceans.

Nictitating membrane

A thin, tough, transparent or translucent membrane, or ‘inner eyelid’, found in various species of birds, reptiles, amphibians and fish, but less common in mammals. The nictitating membrane can be drawn across the eye to protect it from damage, or to moisten the eye whilst maintaining vision.

Pectoral fins

In fish, the pair of fins that are found one on each side of the body just behind the gills. They are generally used for balancing and braking.

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